1. Field of the Invention
The present invention relates to a method of manufacturing axis seals which restrain a flow of fluid in a direction of the rotation axis of a rotary machine such as a gas turbine and the like, axis seals, axis seal members and rotary machines using the axis seals.
2. Description of the Prior Art
A gas turbine which leads high temperature and high pressure gas to a turbine and expands it so as to generate motive power by converting the thermal energy of gas to kinetic rotational energy has a sealing mechanism (an axis seal) mounted thereto between the stationary vanes and the rotation axis in order to reduce an amount of high temperature and high pressure gas leaking from the high pressure side to the low pressure side. Conventionally, non-contact types of labyrinth seals are widely used as the sealing mechanism.
In the labyrinth seals, the amount of leaking gas is large because the clearance space at the tip of a fin must be made large to some extent in order that the tip of the fin will not come into contact during shaft vibration in the transient period of rotation or during transient time of thermal deformation. Leaf seals are developed to take the place of labyrinth seals as mentioned above, aiming at a reduction in the leaking amount.
FIG. 18 is a perspective view of an axis seal (referred as a “leaf seal” hereafter). The leaf seal 9A shown in FIG. 18 consists of a housing 92 which is arranged outside of a rotating axis 91 so as to surround the rotating axis 91; a low pressure side plate 93 which is mounted on the lower side of gas pressure of the housing 92; a high pressure side plate 94 which is mounted opposite to the low pressure side plate 93 and on the higher side of gas pressure; and thin metal plates 95.
The thin metal plates 95 are fitted and engaged into the housing 92 and laminated to the housing 92 in a ring shape. Additionally, the thin metal plates 95 separate the clearance space surrounding the rotation axis 91 into a high-pressure region and a low-pressure region by sealing the periphery of the rotation axis 91. Moreover, on both sides of the thin metal plates 95, the high-pressure side plate 94 is mounted in the high-pressure region and the low-pressure side plate 93 is mounted in the low-pressure region, each of which is mounted as a guide plate in a pressure-acting direction.
The thin metal plates 95 are designed so as to have a predetermined rigidity, which is determined by the thickness of the plate, in a circumferential direction of the rotation axis 91. Additionally, the thin metal plates 95 are mounted to the housing 92 in a manner that an angle made with the circumferential surface of the rotation axis 91 is to be an acute angle against the rotation direction of the rotation axis 91. When the rotation axis 91 stops, the tips of the thin metal plates 95 are in contact with the rotation axis 91 by a predetermined preload. However, when the rotation axis 91 rotates, the thin metal plates 95 and the rotation axis 91 are not in contact with each other because the tips of the thin metal plates 95 are raised by an effect of dynamic pressure caused by rotation of the rotation axis 91.
FIG. 19A and FIG. 19B show the front view and the side view of the thin metal plate 95 respectively. The portion 95d indicated with halftone dot meshing in FIG. 19B is a portion, which is to be eliminated by etching when the thin metal plate 95 is manufactured. When the thin metal plates 95 are laminated, the portions 95d to be eliminated by etching become a clearance space between the thin metal plates 95. In other words, the end portions 951 on the periphery of the thin metal plates 95 are arranged to be in contact with each other, while the end portions 952 on the opposite side of the end portion 951 are arranged so as not to be in contact.
In an axis sealing mechanism and a gas turbine that are constructed as described above, since the thin metal plates 95 having a width in the axial direction of the rotation axis 91 are laminated in a multiple number of layers in the circumferential direction of the rotation axis 91, these thin metal plates 95 have soft flexibility for the rotation axis 91 in the circumferential direction, and an axis sealing mechanism having high rigidity is constructed in the axial direction.
By having the space between the thin metal plates 95 made by the portions 95d where thin metal plates are eliminated, it is possible to arrange the thin metal plates 95 more closely and it is also possible to make the space between the tips of the thin metal plates 95 and the rotation axis 91 significantly small, compared with non-contact type of labyrinth seals and the like, whereby it is possible to reduce the amount of leaking gas to be approximately ⅓ to 1/10 of that of labyrinth seals.
The thin metal plate 95 is formed so as to obtain the predetermined shape by etching a steel plate, which is formed by rolling. At this time, only one side of the thin metal plate 95 is partially etched to be eliminated. However, in case of a thin plate of metal material (e.g. stainless, Inconel, Hastelloy and the like) of approximately 0.1 mm thickness manufactured by rolling, as shown in FIG. 19B, large residual stress (strain) occurs inside the metal material at the time of cold rolling.
When such a material having a large residual stress (strain) inside thereof as described above is thinned by etching only one side thereof in an above-mentioned manner, the distribution of residual stress (strain) becomes non-uniform, causing bending or warp.
For example, as shown in FIG. 20, when assumed tensile stresses are formed on both surfaces of a cold-rolled material and assumed compressive stresses are formed inside thereof, as a whole, the residual stresses on the surface and the residual stresses inside thereof will balance, maintaining the plane. However, as shown in FIG. 21, when a portion 950 of the surface on one side of the thin metal plate 95 is eliminated by etching, residual stresses remain in the central portion 95C and on the surface 95S, excluding the eliminated portion 950. Therefore, by having compressive stress acting on one side (in the central portion 95C) while having tensile stress acting on the other side (on the surface portion 95S), bending moments 9M occur, whereby the thin metal plate 95 warps in a direction toward the eliminated portion 950.
A multiple number of thin metal plates 95 are used for a leaf seal 9A. By having the thin metal plates 95 warped due to residual stress, the leaf seal 9A has portions containing non-uniform space generated here and there, and in these portions, a flow of gas occurs, whereby airtightness of the seal is sometimes lost.
Additionally, since the thin metal plates 95 warp in a direction opposite to the rotating direction of the rotation axis and the like facing to the seal 9A, there arises a possibility of the thin metal plates' 95 contacting with a rotation axis and the like due to shaft vibration during initiation of rotation or during a transition period of rotation such as stopping and the like, or due to a transient thermal deformation.